Is there someone who can help me with some missing characters?

I have played the game many, many times through, but I still have four characters that are not unlocked. The first is the character between Mr. Everett and Olivia in the character list. The other three are on the row immeidately below, the row that concludes with Phoebe Ingram. I thought they were the children from the school, but I've met the children many times and the character list hasn't updated. It just shows ???

The first is Charles Everett but I have not unlocked the three before Phoebe. I can't quite remember how I unlocked this character. I think it was when I was persuing Mr. Curtis at his country house or asking Mr. Everette about Olivia.

Thank you! I thought at one point that I had unlocked all the characters, but that was on a different device that I no longer have. I had to reinstall the game on a new iPad and lost all my previous games. Maybe I need to play through the Mr. Curtis storyline a few different times.